Eyewitnesses described a Jeep Cherokee being driven at speed towards the building with flames coming out from underneath.

They have also described seeing two Asian men, one of whom was on fire, who had been in the car.

Police reported last night that they had arrested three men in relation to the incident.

The airport was evacuated and all flights suspended following the incident at 3.15pm .

A Whitehall spokesman said the incident was not being treated as a national security threat.

One eyewitness said: "I heard the sound of a car's wheels spinning and smoke coming out.

"I saw a Jeep Cherokee apparently as if it was trying to get right through the doors into the terminal building. There were flames coming out from underneath then some men appeared from in amongst the flames.

"The police ran over and the people started fighting with the police.

I then heard what sounded like an explosion."

Eye-witness Richard Gray told BBC News 24: "A green Jeep was in the middle of the doorway burning.

"There was an Asian guy who was pulled out of the car by two police officers, who he was trying to fight off. They've got him on the ground.

"The car didn't actually explode.

There were a few pops and bangs which presumably was the petrol."

Taxi driver Ian Crosby said:

"This was no accident. This was a deliberate attack on Glasgow Airport."

The reaction of members of the public was not to help the men in the car, but to restrain them, he told the BBC. Crosby, who said he served in Northern Ireland, told how he shepherded people away from the scene in case of a secondary explosion or a nail-bomb.

Two men, one of whom was reported to be badly burned, were seen being led away in handcuffs.

Meanwhile anti-terrorism police launched a huge manhunt for the people who planted two car bombs in central London.

Police have described events as "troubling" and are studying hours of CCTV footage in the search for suspects.

Two Mercedes - left outside a nightclub and in a nearby street - were packed with nails, petrol and gas cylinders, but the devices were not detonated.

New prime minister Gordon Brown visited Scotland Yard for an update ahead of a meeting of the government emergencies committee Cobra. A Downing Street spokesman said: "The prime minister was updated on the current security situation and met and thanked the frontline directly."

Police have increased their patrols of the capital and have reviewed security for a number of public events being held in the city, including the Concert for Diana atWembley today.